Wireless sensor networks are networks of small and cheap sensor nodes, which on the one hand provides means (sensors, actuators) to interface with the physical world, and which on the other hand can use wireless technology to locally interact with each other and to increase the robustness of the network. In this talk first a brief introduction to the concept of wireless sensor networks, with consideration of domestic applications. In the second part it is demonstrated by example how the resource constraints found in wireless sensor networks (memory, processing power, radio resources) influence the design of communication protocols.